Does a GUI texture, always have to be 256x256? I tried using one that was 176x176 but the image displayed like it was magnified. I am just curious to know.

I thought so, if you had a large GUI that wouldn't fit onto a 256x256 image, would there be a way around that or would you have to just change it to fit?

Yes. In the drawTexturedModalRect method is are two values: f and f1. Those floats represent the image width and height. To get these values you devide 1 by 256, the image size. So to make a larger image possible, copy that method, and change f and f1 to be 1/imageWidth and 1/imageHeight.

You can use this custom method that does not need a 256x Texture

 

public static void drawTexturedQuadFit(double x, double y, double width, double height, double zLevel)
{
Tessellator tessellator = Tessellator.instance;
        tessellator.startDrawingQuads();
        tessellator.addVertexWithUV(x + 0, y + height, zLevel, 0,1);
        tessellator.addVertexWithUV(x + width, y + height, zLevel, 1, 1);
        tessellator.addVertexWithUV(x + width, y + 0, zLevel, 1,0);
        tessellator.addVertexWithUV(x + 0, y + 0, zLevel, 0, 0);
        tessellator.draw();
}

Great, thank you. I am trying to learn about GUIs so this i very useful to know.